1. Field of the Invention
The invention relates to a system for determining the height of a tripod-mounted geodetic tool above a reference area-to a spacer and a distance measuring device for such a system.
2. Description of the Related Art
For surveying tasks using geodetic tools, it is necessary to know, for example, the height of the optical axis of the tool above a reference area. The reference area is defined by a geodetic point of reference (reference point) which is marked, for example in a boundary stone.
In DE 40 07 245 A1, a laser apparatus mounted on a tribrach prior to assembly and intended for perpendicular positioning above the reference point is used. The height of the device above the reference point is then to be determined using the laser. Reference points are, for example, generally marked in a boundary stone by indentations or notches. The reference plane is however defined by the maximum projection of the boundary stone. The measurement by means of a laser beam is therefore inaccurate.
Other systems use measuring tapes in the form of roll-type tape measures. The roll-type tape measure is fastened to an adapter (height measuring bracket, height hook) so that it is present in the plumb line above the reference point during the measurement. Known adapters are fastened by means of a spindle in a centering bush of the tool and run around the tripod and the tripod head into the plumb line. An operator pulls the tape measure out of the roll-type tape measure and runs it to the boundary stone. The height of the tool is indicated on a mark on the roll-type tape measure. The measuring procedure is difficult and susceptible to inaccuracies because, on the one hand, the end of the roll-type tape measure has to be held by the user on the boundary stone and, on the other hand, the mark has to be read at a height. Wind-related inaccuracies may also occur. Such adapters consist of metal and are relatively bulky. This make them problematic to transport.
U.S. Pat. No. 5,720,106 describes a measurement of the slope height of a tripod-mounted geodetic tool above the reference area outside the plumb line. Here, however, it is the uncorrected slope height that is indicated on the mark to be read on the roll-type tape measure. The true height of the geodetic tool above the reference area can be calculated based on the slope height and the on the geometrical relationships of the tripod-mounted geodetic tool.
It is the object of the invention to provide a system of the type stated at the outset for determining the height of a tripod-mounted geodetic tool above a reference area, which system gives sufficiently accurate measurement using simple means.
The arrangement, according to the invention, departs from the principle of measuring inside the plumb line. Instead, the measuring distance makes an angle with the plumb line. By a suitable design of the scale, the perpendicular height above the reference point can nevertheless be read with sufficient accuracy.
On the one hand, a roll-type tape measure which is fastened to a spacer attached to the tribrach or to the instrument, drawn downward and placed against the reference area relative to the point of reference is suitable for the length measurement. The scale on the graduated tape of the roll-type tape measure is adapted and shows not, for example, the length of the measured distance but directly the required perpendicular height of the tool above the point of reference. Alternatively, it is possible to use a measuring stick, for example a plumb bar, which is placed on the reference area in the vicinity of the reference point and is to be read at the spacer. The scale mounted on the plumb bar in turn indicates the perpendicular height. The spacer has relatively small external dimensions compared with known adapters, while roll-type tape measure and plumb bar are in any case carried by the user of the geodetic tool in the standard equipment.
The scale of the roll-type tape measure or plumb bar has nonlinear divisions andxe2x80x94provided that the spacer is aligned horizontallyxe2x80x94is calculated using Pythagoras"" law, which relates the lengths of the sides of a right-angled triangle to one another. The catheti of the right-angled triangle are formed by the distance from the point of engagement or end of the spacer to the plumb line and the height of this spacer plane above the reference area at the reference point along the plumb line. The hypotenuse of the right-angled triangle is given by the distance between the reference area at the reference point and the end of the spacer. If it is not intended to arrange the spacer horizontally on the tool, the scale of the measuring device coordinated with the spacer, whether roll-type tape measure or plumb bar, is calculated in a correspondingly different manner. What is advantageous is that it is not necessary for the measuring spindle, the measuring blade or a stop of the roll-type tape measure or an end of the plumb bar to be placed directly on the reference point on which the plumb line stands, but can be positioned slightly outside. The resulting inaccuracy of the measurement can be neglected. Rather, the roll-type tape measure or the plumb bar can now be placed on the highest point of the reference point, for example of the boundary stone which defines the reference plane.
If, for example, a roll-type tape measure which is also to be used for measuring lengths other than the height of the tool is now used for measuring the length, application of the nonlinear scale in coded form is then possiblexe2x80x94in order to avoid uncertainties in reading. This is also true for the use of an inch rule.
In the context of the present invention, xe2x80x9ccoded representationxe2x80x9d of a scale is intended to mean representations which can be read not directly but only indirectly, whether, for example, by interspersing a mirror (in which case the scale representation is mounted as a mirror image on the scale support), whether via special color filter (in which case the scale representation is in false colors and cannot be differentiated with the naked eye) or whether by interspersing an anamorphotic lens (in which case the scale is mounted with distortion and defocusing). The above examples for coded representation are not definitive. Thus, for example, the provision of reading slides or windows with staggered grid is possible which permits reading of the scale only in cooperation with an opposite grid making it difficult or impossible to read the scale on the scale support directly.
If, for example, a scale is mounted on the scale support in the coded form described above, it can be read only using the corresponding reading means. If the operator attempts to read this coded scale at the reading mark which is coordinated with the scale mounted in uncoded form, the error will be directly evident. Reading is difficult if not impossible. In a corresponding manner, a reading error is avoided for the scale mounted in uncoded form if the operator attempts to read this scale using the reading means.
With the use of a cylindrical lens whose axis runs along the scale support, a compressed scale which is readable only by means of the cylindrical lens can be mountedxe2x80x94preferably in the middle of the scale support. Above and below the compressed scale, which is visible to the naked eye only as a dotted line, in each case directly readable and optionally further, only indirectly readable scales can be mounted. The compressed scale can in this case simultaneously serve as a separating line for different scales above and below it.
Since in general only a relatively small scale region can be read using the reading means, measures are taken to ensure reading which is as error-free as possible. This is achieved, for example, by specially designed scales and/or the magnification of the reading region.
Thus, the scale can be modified in such a way that, even in a relatively small reading region, it is clearly visible in which direction of the scale the numbers are arranged in ascending order.
The housing need not be made larger in order to increase the size of the reading region. The reading region can be broadened, for example, by providing a mirror which is inclined at an acute angle instead of at an angle of 45xc2x0. The image of the scale is thus compressed and a reading errorxe2x80x94due to divisions to be read as mirror imagesxe2x80x94is avoided because several numbers arranged in ascending order corresponding to the scale of the graduated scale appear in the field of view.
Alternatively or in addition to the mirror inclined at an acute angle, it is also possible to use a concave mirror or a corresponding concave prism in order to compress the scale. Furthermore, a scattering lens may be present before a mirror. Although this leads to slight distortions at the edge of the field of vision, depending on the quality of the mirror or the lens, said distortions do not adversely affect the reading.
A similar result is obtained if the running surface on which the scale support moves past the reading mark is not flat but curved. The scale appears compressed and will have small distortions in the edge regions. The distance from scale support to reading mark will have to be kept as small as possible and constant.
The scales can be mounted both on opposite sides of the scale support and on the same side. The scales differ, for example, in having different starting points to which the graduations noted along the scale relate. The scales can also have different linear or nonlinear dependenciesxe2x80x94based on the length to be measured. In general, the invention can be advantageously applied when scale graduation and marking (apart from the coded representation) of different scales are not identical. Thus, it would be possible to use this systemxe2x80x94independently of the application described herexe2x80x94also for angle-measuring instruments (degree or radian graduation) or velocity-measuring instruments (kilometers or miles per hour).
The reading marks coordinated with the different scales, for example for roll-type tape measures, can be arranged at different points of the housing. The distance between the two marks is at least sufficiently large that good readability is ensured and the marks can be sufficiently clearly distinguished by the operator.
The scale mounted in coded form on the scale support is expediently located xe2x80x94for roll-type tape measuresxe2x80x94on the side which, when rolled up on the scale support, the scale tape roll, faces outward. The reading means is then fastened in the housing wall, opposite the roll.
Expediently, the scale supportxe2x80x94for roll-type tape measuresxe2x80x94is passed along a running surface or over a gangway opposite the reading mark of the reading means. The distance between mirror and scale support remains the same, regardless of the drawn-out length of the scale tape. Parallax when reading is thus reduced. In order practically completely to rule out the reading error due to parallax, a reading mark is applied not only on that side of the reading means which faces the scale support but also on the side facing the user.
The running surface furthermore results in a constant draw-out angle because the scale support in any case runs over this.
The reading mark is expediently a clearly readable line marked in color.
The measuring device according to the invention permits selective reading of the individual scale, which must be performed in a deliberate manner, makes the reading reliable and prevents mistakes. The roll-type tape measure used in the case of the height-measuring tool according to the invention can of course also be used quite normally in the usual way as a roll-type tape measure without mistakes occurring in the reading.
The scale tape can be held taut by the operator. Even in a strong wind, the accuracy of measurement is thus maintained.